It is known that the chemical structure of a polymer conditions its physicochemical properties. For example, polymers including one or more ethylenic double bonds, hereinafter denoted by unsaturated polymers, are flexible and elastic. For this reason, they have many applications.
However, their applications are limited as the ethylenic double bonds are sensitive to oxidation, which renders unsaturated polymers unstable with regard to thermal and/or UV aging.
On reducing the degree of unsaturation of unsaturated polymers, their sensitivity to oxidation is reduced. The reduction in the degree of unsaturation is generally carried out by hydrogenation.
For some applications, it is necessary to find a compromise between the elasticity of a polymer and its sensitivity to oxidation. Hence the advantage of a controlled hydrogenation technique.
The hydrogenation method and the reactions employed are known and widely described. Mention may be made of some, by way of indication.
WO 00/009576 discloses the use of a system comprising hydrazine, an oxidizing agent and a catalyst comprising an element from group 13 of the Periodic Table for the hydrogenation of unsaturated polymers, such as elastomers based on nitrile and on butadiene denoted by NBR.
U.S. Pat. No. 5,302,696 discloses a process for the hydrogenation of latex by the use of hydrazine, an oxidizing agent and an iron or copper salt. Application to the NBR latex.
WO 91/06579 discloses a preparation of coagulated rubber comprising little unsaturation from an NBR latex hydrogenated in the presence of hydrazine and of an oxidizing agent.
U.S. Pat. No. 5,902,889 discloses a process for the hydrogenation of unsaturated fatty acids in aqueous solution in the form of salts by hydrazine in the presence of an oxidizing agent and of a metal salt.
U.S. Pat. No. 5,442,009 discloses a process for the preparation of a hydrogenated “dry” rubber by hydrogenation of a latex in the presence of an oxidizing agent, of hydrazine and of a metal salt. Application to NBR latexes.
U.S. Pat. No. 5,424,356 discloses the preparation of hydrogenated rubber by the treatment of a latex (NBR) with an oxidizing agent in the presence of hydrazine and of a metal salt.
WO 92/17512 discloses the hydrogenation of unsaturated latexes in the presence of an oxidizing agent, hydrazine and a metal salt. The latexes cited are (I) butadiene, (II) acrylonitrile, isoprene or butadiene and/or (III) styrene copolymers.
U.S. Pat. No. 4,452,950 discloses the hydrogenation of the double bonds of an unsaturated polymer in the form of a latex in the presence of hydrazine, of an oxidizing agent and of a metal salt.
As may be observed, all these documents disclose a hydrogenation process based on the presence of a metal salt.